1. Technical Field
The present invention relates generally to security systems and in particular to a system for detecting and tracking the position of a door. More particularly, the present invention relates to a method and system for remotely tracking the position and cyclic change of position of a door or other access portal member.
2. Description of the Related Art
Door security sensors are implemented in home or building alarm systems to detect and monitor the relative position of doors, windows or other building access structures as being either secure (e.g. closed) or unsecure (e.g. open or partially open). Such systems typically employ electronic monitoring means to sense the relative disposition of the door. On the user notification side of such systems, output devices in the form of light-emitting diodes (LEDs) and/or audio output devices are utilized to alert occupants either that the door remains secured or that the door has become unsecured (i.e. opened from a secure closed position) in accordance with the received sensor signals. The monitoring and tracking of entryway portal security status may be communicated to the local building occupants and may also be broadcast outside the building using siren-like alarms, or delivered to specified point locations using electronic signaling to notify remote persons or security agencies of a compromise in doorway security.
Conventional door monitoring systems often utilize transmitter/receiver pairs wherein the transmitter transmits a sensed door position signal to a strategically positioned receiver that in turn outputs the corresponding status or alert signal. Wireless transmitter/receiver pairs, typically using an RF communication medium, are utilized in some door monitoring applications for ease and flexibility of implementation. One such system is described in U.S. Pat. No. 5,798,681, issued to Chang, which discloses an RF-based garage door position indicator. The disclosed system of Chang employs an electronic angle sensor that is attached onto the garage door and supplies door position signals to an RF transmitter corresponding to sensed changes in orientation in the garage door from vertical to horizontal and from horizontal to vertical. The Chang system further includes an RF receiver, remotely mountable as a portable unit in a vehicle or otherwise, which is responsive to the door position signals and controls a visual/audio output accordingly.
While effective for sensing the door position and providing user alert responses, prior art door monitoring systems do not account for RF compliance with FCC continuous or periodic transmission. Furthermore, there exists a need, unsatisfied in the prior art, to implement a portable RF receiver door monitor receiver in a manner that adequately conserves battery power. The present invention addresses these and other needs unsatisfied by prior art door monitoring systems.